1. Field of the Invention
The invention relates to improvements in rockingbeam type furnaces for heating billets or the like.
2. Description of the Prior Art
As is known, rocker-bar type heating furnaces, sometimes called walking beam heating furnaces, are provided with axed support beams which extend lengthwise of the interior of the furnace, and with conveyor beams which are parallel to the fixed beams and which can be raised and lowered and moved back and forth. The movement of the billets through the furnace is effected intermittently by raising, shifting in the direction of passage and depositing the billets, the conveyor beams being raised until their upper edges project above the upper edges of the fixed beams, causing the billets to be raised from the fixed beams and to rest on the conveyor beams. Subsequently the raised conveyor beams are moved in the direction of the delivery port of the furnace, the billets being thus moved onward by a corresponding step. Then the conveyor beams are lowered again to such an extent that their upper edges are below the upper edges of the fixed beams, causing the advanced billets to be again deposited on the fixed beams. The lowered conveyor beams are finally returned for carrying out the next conveying step.
With furnaces of this type as known, for example, from German Pat. No. 1,221,260, the billets are conveyed through the furnace parallel to themselves in such a manner that they always face upwards with the same surface. With these furnaces the upper horizontal billet surface is heated much more quickly than the lower horizontal billet surface. As a result of the temperature difference between the upper and the lower billet surfaces the billet will arc vertically outward towards the top. But also the forward vertical billet surface as seen in the direction of travel will be heated more rapidly and intensely than the rear vertical billet surface as the hotter furnace zones are located in the discharge end section of the furnace. Due to the temperature difference resulting therefrom between the forward and rear billet surfaces the billet will also arc forward in a horizontal direction. The vertical, more particularly the combined vertical and horizontal billet deflection or deformation, caused by the difference in temperature of the opposite billet surfaces can assume such proportions that the billets tip over in the direction of travel. This complicates and occasionally completely prevents the discharge of the heated billets from the furnace, and often the operation of the furnace must be interrupted in order to eliminate these faults, i.e. to restore the deformed and tipped-over billets to their proper position by external means. In order to overcome these difficulties, the known methods of heating billets in rocking-beam type heating furnaces make it necessary to step up the heating of the billets gradually until the desired temperature has been reached, i.e. to use correspondingly long heating furnaces or to increase the passage time of the billets through the furnace.
It is an object of the invention to eliminate these drawbacks and to develop a method of heating billets or the like in rocking-beam type heating furnaces, by means of which undesirable or excessive deflection or deformation, caused by excessive temperature differences between opposite sides of the billet surfaces, with consequent tipping movements of the billets in conjunction with shorter passage times of the billets through the furnace or in conjunction with a greater specific heat intake of the billets per unit length of the furnace is avoided.